That was one among many moment where it shit the bed to me. Several other moments are why any character is so lenient on sparing some characters. It's just not a terribly well-planning comic. Character go from horrible to redeemed to starting shit and then forgiven. It's like shoot-first-and-ask-questions-later all over the place. The sheer erraticism of Mark alone later in the story would have justified him being murdered first among all the other characters who die.
It felt, unsurprisingly, exactly like The Walking Dead. I dare say between Walking Dead and Invincible that Kirkman has a style, a profoundly shitty style that makes his comics dogshit the longer they go in that characters start shit for the sake of starting shit.